1,3-Propanediol is a precursor for polyether glycols, polyester bomopolymers and copolymers, and thermoplastic elastomers. The quality of these products is in general dependent on the quality of the raw materials. For some applications, such as fibers, color quality is a major concern. It is known that products derived from 1,3-propanediol have suffered from discoloration. Commercially available samples of 1,3-propanediol starting materials have resulted in brown colored polyether glycols. Disclosed attempts to remove color from the products made from available 1,3-propanediol have been laborious and expensive. Even after extensive purification processes, many products retain a yellow color.
U.S. Pat. No. 2,520,733 discloses a process for the purification of polyols prepared from 1,3-propanediol in the presence of acid catalyst (2.5 to 6% by weight) and at a temperature from about 175.degree. C. to 200.degree. C. This purification process involves percolation of the polymer through Fuller's earth followed by hydrogenation. Even after this extensive purification process, the final product remains light yellow in color.
U.S. Pat. No. 3,326,985 discloses a procedure for the preparation of poly(1,3-propanediol) of molecular weights in the range of 1200-1400 possessing improved color by vacuum stripping, under nitrogen, poly(1,3-propanediol) of lower molecular weight.
U.S. Pat. No. 5,659,089 discloses a process for the preparation of poly(2-methyl-1,3-propanediol) by the etherification of 2-methyl-1,3-propanediol. No diol purification process is given. Any available grade of diol can be used in the etherification process.
U.S. Pat. No. 5,527,973 discloses a process for providing a purified 1,3 propanediol which can be used as a starting material for low color polyester. That process has several disadvantages including the use of large equipment and the need for dilution with large quantities of water which is difficult to remove from the product.
The process of the present invention alleviates the problem of discolored polymer production in a relatively simple and economical process. The process of the present invention involves purification of, and removal of color precursors from the starting reactant 1,3-propanediol rather than treating the resulting products. The purified diol from this process is useful for preparing a variety of polymers that include polyether glycols, polyesters and thermoplastic elastomers having excellent color characteristics.